The invention relates to a magnetic control system for circular knitting machines, intended for pattern-true control of selector elements, which may be tipped about a bearing surface forming part of pivot means, extending in their direction of travel, comprising several electromagnets of which each has at least one pair of polar surfaces acting on the selector elements and where the polar surfaces have different spacings from this bearing surface.
Different magnetic control systems, of the aforesaid kind, for circular knitting machines, have already become known in which the period available for performance of the selecting operation is extended by the application of several electromagnets; two variations are possible in this connection: in the one variation, for example as disclosed by DT-OS 2,217,115, published on Oct. 26, 1972 which corresponds to U.S. Pat. No. 3,851,500, each selector element runs past the pairs of polar surfaces consecutively, and the electromagnets are energized in chronological sequence, whereas in the case of a second variation, selector elements of several types are applied, the number of types corresponding to the number of electromagnets, the different selector element types have several butts at different points for cooperation with the electromagnets, and the electromagnets are situated at different distances from the bearing surface depending on the position of these butts, so that the electromagnets may in each case act on one selector element type only during simultaneous energization, the period available for the selecting operation may thus be multiplied according to the number of electromagnets or of selector element types. It is apt to add moreover, that in the case of the second variation, the butt of the selector elements cooperating with one of the electromagnets in each case is situated at different levels in the different selector element types.
In both forms, the effective lever arm of the different electromagnets with respect to the bearing surface is then varied so that the selector elements may be tipped. This is extremely disadvantageous, because efforts are obviously made in view of heat generation, to rate the power of the current pulses for the electromagnets at a minimum, and on the other hand, the fast-running modern circular knitting machines require relatively great selection forces, so that selection and thus pattern faults may be prevented reliably. Consequently, in the case of the known magnetic control system, it is the electromagnet having the shortest distance from the bearing surface which determines the power of the current or rather control pulses, if a complicated control system having different pulse levels for the different electromagnets is to be dispensed with.